default content-type should be Text

While developing the content-type feature I misread
the docu and tought that 'None' is the no-highlighting
content-type. But its acutally Text.
Merge pull request #24 from darinkes/text_content

default content-type should be Text
limit lines in preview to 10

Instead of limiting the chars we should limit the lines.
It's more readable and also makes highlighting for pygments
more reliable.
add upload file and content detection

Add the possibility to create a new post by uploading
a file and autodetect its content-type.

If the user uploads a file and enter s.th. in content
they get combined.

If the user leaves the title blank and uploads a file
the filename is used as title.
Merge pull request #25 from darinkes/limit_lines

limit lines in preview to 10
fixes for upload-file

- content-type "None" does not exist.
- set the title to filename if blank correctly